Cam clutch with ball retaining and guiding means



March 8, 1960 L. A. AMTSBERG 2,927,445

CAM CLUTCH WITH BALL RETAINING AND GUIDING MEANS 2 Sheets-Sheet 1 FiledOct. 20. 1958 T aa5 .22

ATTORNEY March 8, 1960 L. A. AMTSBERG 2,927,445

CAM CLUTCH WITH BALL RETAINING AND GUIDING MEANS Filed Oct. 20, 1958 2Sheets-Sheet 2 W h M ATTORNEY United States Patent CAM CLUTCH WITH BALLRETAINHVG AND GUIDING MEANS Lester A. Amtsherg, Utica, N.Y., assignor toChicago Pneumatic Tool Company, New York, N.Y., a corporation of NewJersey Application October 20, 1958, Serial No. 768,096

11 Claims. (CI. 64-29) This invention relates to cam clutches of thetype which release automatically due to the camming action of a set ofballs normally seated in pockets in the driving and driven plates, saidballs being arranged, on developmentof a predetermined torque, to climbout of the pockets and hold the clutch plates temporarily separatedwhile the balls are overrunning from one set of pockets to the next. Theinvention is concerned particularly with the means for maintaining theballs in uniformly spaced relation during the overrun period in order toassure that all balls will re-register at the same time with thesucceeding pairs of pockets, and thereby permit the clutch plates toreengage.

This case is a continuation-in-part of applicants prior applicationSerial Number 600,876, filed July 30, 1956. As disclosed in thatapplication, the ball cam clutch forms part of a machine for drivingscrews, nuts or bolts to a predetermined tightness and cooperates with asecondary clutch and control mechanism arranged to kick out thesecondary clutch and interrupt the rotation of the driven screw inresponse to the movement of the ball cam clutch, first in the separatingand then in the re-engaging direction. It is important that the clutchre-engage quickly and completely following the separation and period ofoverrun. In some prior devices of this kind, the reengaging action hasbeen unreliable under certain conditions due to the fact that the balls,in rolling over the faces of the driving and driven plates, do nottravel exactly the same distance or over the same path, and get out oftheir uniformly spaced relation with the result that when one ballregisters with a pair of pockets, another ball is out of registry withits associated pockets and prevents the clutch plates from reengaging.Attempts have been made to hold the balls in proper spaced relation bymeans of a retainer. The conventional retainer, however, being in theshape of a disc, takes up space between the driving and driven clutchplates, making it necessary to reduce the depth of the pockets.

An object of the present invention is the provision of means forretaining and guiding the balls during their overrunning movement fromone set of pockets to the next, so as to insure accurate alignment ofall of the balls simultaneously when they re-register with the pockets.

A further object is the provision of a ball retainer which does notrequire the driving and driven clutch plates to be spaced far apart tomake room for the retainer. In accordance with this invention theretainer is in the form of a cylindrical cage adapted to project withincylindrical recesses in the driving and driven plates, said cagepermitting the clutch plates to remain in closely spaced relation bothinside and outside the cage.

A feature of the invention is a set of radial ports provided in thecylindrical cage, said ports being of suflicient axial length to provideproper support for the ma l or idlecondition of the parts as shown inFig. 1,;

balls and being of suflicient diameter that the balls may be readilyinserted or removed when the parts are being assembled or disassembled.Due to the fact that the retainer cage in itself does not prevent theballs from moving radially, it has been found necessary to In theaccompanying drawings which illustrate one embodiment of this invention:

Fig. 1 is an enlarged longitudinal half section of a ball cam clutchembodying this invention, with the clutch plates together as in idlecondition;

Fig. 2 is a view similar to Fig. 1 with the clutch plates momentarily inseparated condition;

Fig. 3 is a plan view, partly in section, of the retain-' ing cage forthe balls;

Fig. 4 is a longitudinal section of the retainer cage taken on the line4-4 of Fig. 3;

Fig. 5 is a longitudinal section of the upper or driven plate of the camclutch taken on the line 55 of Fig. 6;

Fig. 6 is a bottom view of the driven plate of the cam clutch;

Fig. 7 is a fragmentary view similar to Fig. 6 but on a larger scale;

Fig. 8 is a plan view of the lower'or driving plate of the cam clutch;

Fig. 9 is a cross section of the driving plate taken on line 9-9 of Fig.8;

Fig. 10 is a fragmentary view similar to Fig. 8 but on a larger scale. 7

Figs. 1, 2, 7 and 10 are drawn to a scale which is double that of theother figures.

Referring to Figs. 1 and 2, the cam clutch comprises a driving plate 12and a driven plate 13. The latter is supported in a connterbore 14 in arotatable driving cup 15. Interposed between the top of the drivenclutch plate and the bottom wall of the driving cup is a roller thrustbearing 16. The latter cooperates with resilient means (to be describedlater) to prevent the driven plate 13 from moving axially relative tothe driving cup 15, but to permit relative rotation. The driving cup iskeyed to a spindle 17 and rotates continuously therewith. Below thecounterbore 14, the driving cup has integral fingers 18 engaging a pairof lugs 19 (Fig. 8) provided on opposite sides of the driving clutchplate. The fingers constrain the driving clutch plate for rotation atthe same speed as the driving cup 15 but permit relative axial movement.Such movement is resisted by a heavy spring 20, the upper end of whichprovides a seat for the driving clutch plate and the lower end of whichis seated on an inturned flange 21 (Fig. 2) formed on a spring retainersleeve 22 which surrounds the spring. The upper portion of the retainersleeve has a threaded connection 23 with the driving cup 15, whereby thesleeve, on being turned, may adjust the amount of compression of thespring and, therefore, the force with which the driving clutch plate 12is urged upwardly toward the driven plate 13.

The force of the spring is transmitted from the driving plate 12 througha set of balls 24 to the driven plate 13 and through the roller thrustbearing 16 to the driving cup 15. All balls 24 are of the same size. Inthe nor- Patented Mar. 8, 1960 over long pec 3 7 1 each ball rests atthe bottom of a recess or pocket 25 in the clutch driving plate 12 andin a correspondingly shaped recess or pocket 26 in the clutch drivenplate 13. The pockets are all of the same size, and at the same distancefromthe axis of rotation and are uniformly spaced from each other.Accordingly, when one pair of pockets register, all pairs register. Anannular groove 27 connects the pockets in the drivingplate 12 andprovides a raceway for the balls in rolling from one pocket 25 to thenext as shown in Fig. 2. A similar annular groove or raceway 28 isprovided in the driven clutch plate 13 to provide a raceway connectingthe pockets 26 in the driven plate 13.

The parts of the clutch, here disclosed, rotate in uni son in therelation shown in Fig. 1 while the spindle 17 is being driven through-asuitable motor and gear reduction (not shown) and while the teeth 29 onthe driven clutch plate 13 are connected to a screw, nut or bolt (notshown) which offers only moderate resistance to rotation. All of thetorque is transmitted through the driving pockets 25, the balls 24 andthe driven pockets 26 and these elements due to their shape act as a camto set up an axial component of force tending to separate the clutchplates 12 and 13. When the driven screw becomes seated and itsresistance to rotation increases to the maximum amount, which ispredetermined by the adjustment of the spring retainer sleeve 22, theaxial component of force between the clutch plates, being proportionalto the rotary component, increases sufiiciently to overcome the spring20 causing the driving clutch plate 12 to move down along the fingers18, thereby permitting the balls 24 to climb out of the pockets 25 and26.

After leaving the pockets, the balls roll along the raceway 28 of thedriven clutch plate 13 while the raceway 27 in the driving plate 12rolls over the balls. The overrunning action continues, with the partsin the Fig. 2 position, until the driving clutch plate 12 has overrunthe balls 24 by an angular distance corresponding to the space betweentwo adjacent pockets, and the balls have overrun the driven plate 13 bya corresponding distance. At the end of the overrun period, each ballregisters. with a new set of pockets. The driving clutch plate, 12 isthen restored to its upward position by the action of spring 20, and allof the parts of the clutch, which are illustrated in full lines, resumethe position of Fig. 1.

The driving clutch plate 12 is provided with an annular recess30.adapted to register with and receive alocking detent 31 when thedriving plate 12 is lowered to the Fig. 2 position and to raise thedetent when the driving plate is restored to the position of Fig. l.

The structure and mode of operation described up to this point areessentially the same as in applicants prior application Serial Number600,876, to which reference may be made for a more detailed descriptionof the complete machine, in which the present invention, may be applied.As explained in that application, the locking detent 31 forms part of adevice for kicking out a secondary clutch when the detent is raised fromthe Fig. 2 position, whereby further rotation of the driving Fig. 1 tothe Fig. 2 position in response to a predetermined, torque, remainsseparated or disengaged for a. brief interval of time and'then reengagesto the Fig. 1 position. III-represent invention, however, does relate tothe-length ofgtim'ethat the clutch plates. are maintained intheseparated condition of'Fig. 2.

As shown in Figs; 6 and 7, the driven pockets 26 are not spaced; asclosely as possible to each other, as theyarein some priorartconstructions, but are separated by" a substantial length of racewayportions 28, thus requiring a finite interval of time during the passageof the ball from one pocket to the next, the time being sufficient topermit the ball detent 31 and associated kickout mechanism (not shown)to become efiective. A similar space between the driving pockets 25 isshown in Fig. 8. The substantial circumferential spacing of the pocketscreates a new problem when the clutch rotates at high speed, forexample, 2,000 revolutions per minute, because the rapidly descendingclutch plate 12 sometimes overshoots due to inertia and loses contactbetween the annular raceways 27 and 28 and the balls 24. When the ballslose contact with the raceways, they sometimes move at slightlydifferent speeds and become un-uniformly spaced. When this happens, itis possible for one ball 24 to register with its associated pockets 25and 26 while another ball is out of registry with its pair of pockets,thus preventing engagement of the clutch plates.

Attempts have been made to solve this problem by providing a retainer tomaintain the balls uniformly spaced, to correspond to the uniformspacing of the. pockets. The use of a conventional retainer, while.solving one problem, however, creates another because it takes upspace, in an axial sense, between the opposed faces of the driving anddriven plates 12 and 13. Tait-- ing up space for the retainer makes itnecessary to shorten the depth of the pocket and reduce the angle at theedge of the pocket. This reduces the maximum torque unless compensatedfor by the use of a more powerful spring; which in turn would increasethe bulk of the machine.

The present invention solves the problem of keeping the balls uniformlyspaced in a circumferential sense, without making it necessary to takeup space between the opposed faces of the driving and drivenclutchplates.

According to the present invention, the retainer ele-* ment is in theshape of a cylindrical cage or sleeve 32. The upper part of the cage isloosely fitted within a cylindrical recess 33 formed in the upper ordriven clutch plate 13. The cage is mounted for rotary and axial, butnotradial, movement relative to the walls of the cylindrical recess 33. Theupper cylindrical recess extends through the centers of the pockets 26and of the raceways 28, as shown in Figs. 5, 6 and 7. The lower por tionof the cage is loosely fitted within a cylindrical recess 34 formed inthe driving clutch plate 12. The shape.

and arrangement of the cylindrical recess 34 is similar:

to that of the upper cylindrical recess 33. At its midportion, cage 32has a plurality of radial bores 35, each of cylindrical shape and havinga diameter slightly ex-.

ceeding that of the balls 24. As shown in Fig. 3, there.- are eightradial bores 35, spaced 45 apart, but the numr ber may be varied,provided that the radial bores are"- circumferentially spaced by auniform angle correspond, ing to the angle spacing the pockets 25 and26.

The operationof the retaining and guiding means of this invention is asfollows: Upon development of a.

predetermined torque reaction transmitted through, the

teeth 29 to the driven cam plate 13, the driving plate:

12 moves down from the Fig. 1 to the Fig. 2 position, and the balls 24move out of the pockets 25, 26 into the raceways 27, 28 as previouslydescribed. The con; tact between the balls and the walls of the retainerbores.- 35 is sufficiently loose to permit the balls to roll freely.

Under ordinary conditions, the balls remain in rolling engagement withthe raceways until the driving plate' 1.2,

rotates 45 ahead of the balls 24 and the latter rotate-45,

ahead of the driven plate 13, making a total of rotation of the drivingplate ahead of the driven plate,,whereupon, the clutch reengages to theposition shown in Fig. 1,, The; continuous engagement between the,balls, 24, and: raceways 27, 28 is ordinarily sufiicient to cause all.of. the balls to roll the same distance over the. raceways atthesametime and thereby maintain a' uniformly spaced, circumferential relationso that when one ball" registers, with the succeeding pair of pocketsall the other balls register in the same manner. Under conditions ofhigh speed and high axial inertia of the driving plate 12, however, theclutch plates may be spaced apart momentarily by a greater distance thanthe amount shown in Fig. 2 and one or more of the balls may lose contactwith the raceways 27, 28. However, the retainer cage 32 positivelyprevents the balls from getting out of the uniform circumferentiallyspaced relation. The retainer cake is free to float in a vertical oraxial direction, its position being determined by that of the balls 24.That is to say, the cage follows the downward movement of the balls fromthe Fig. 1 to the Fig. 2 position by moving downward a correspondingamount in the cylindrical recess 33. At the same time the lowercylindrical recess in the driving clutch plate 12 moves downward withrespect to the retainer. The speed of rotation of the retainer cage isalso controlled by the balls, being less than that of the driving plate12 and greater than that of the driven plate 13 when the parts are inthe overrunning condition of Fig. 2. Radial movement of the retainercage is prevented by the frictional engagement with the walls of thecylindrical recesses 33 and 34. The retainer cage 32 does not in itselfinclude any means to prevent the balls 24 from moving out of theircircular orbit. However, movement of the balls toward or away from theaxis of rotation of the clutch is prevented by the arcuate grooves 27,28.

As stated previously, each driving pocket 25, which nornially registerswith'an associated driven plate 26 will,

upon displacement and overrun, re-register with the last driven platefollowing 90 of rotation of the driving plate 12 ahead of the drivenplate 13. At the time the pockets re-register, the balls will have beendisplaced by the same number of degrees, usually 45 in which case theparts will be restored to the Fig. 1 position. If, however, the ballshave rotated slightly more or slightly less than 45 since their lastregistry, they will engage the sides of the pockets with a cammingaction to cause a slight relative rotation between the retainer cage 32and the clutch plates 12 and 13, until the balls register exactly withthe pockets.

The retainer cage 32, due to its shape, permits the faces of the drivingand driven clutch plates 12 and 13 to be spaced closely to each other asshown in Fig. l, and therefore permits the effective portion of thepockets 26 to extend for nearly 180 or over a zone approximating ahemisphere. As shown in Figs. 5, 6 and 7, part of the pocket 26 is cutaway to provide a cylindrical recess 33 for receiving the retainer cage32. However, the interruption or discontinuity of the cam surface of thepocket does not materially impair the function of the pocket because theremaining surface is sufiicient to provide the necessary cam action.Also a portion of the raceways 27 and 28 is cut away to provide thecylindrical recesses 33 and 34, but the loss of raceway area is notaccompanied by any loss of function because the central portion of theraceways is not effective as a guide in keeping the balls within theircircular orbit.

If desired, a crescent shaped chamfer 36 may be provided along the edgeof the driven pocket 26 and a similar chamfer 37 (Fig. may be providedalong the edge of the driving pocket 25, to make the balls 24 disengagemore readily from the pockets when they roll over the chamfered edges,than when they are driven in the opposite direction and roll over theedges which are not chamfered. The purpose of the chamfer is to make theclutch release at a slightly lower torque when driven in a direction totighten the screw than when driven in a loosening direction. With thisarrangement it is always possible for the operator to remove a screwafter driving it to a predetermined tightness, without the clutchdisengaging during the loosening operation and without changing theclutch adjustment to a higher torque value.

The annular grooves or raceways 27 and 28 should have a radius in crosssection equal to that of the balls 24 to provide maximum area of contactwith the balls and to minimize wear. The pockets 25 and 26 should have aradius equal to or slightly greater than that of the balls. If theradius is the same, the ball contacts the entire hemi-spherical surfaceof the pocket except where the latter is cut away. With this arrangementof equal radii, the driving action and also the camming action of thepocket occurs over a relatively large area of the ball, and the latter,upon starting to climb out of the pocket, completes the declutchingaction rather suddenly. If the pocket has a greater radius than theball, however, the driving and camming force is transmitted to the ballover a relatively small pocket area at any one time. The oversize pocketarrangement introduces lost motion between the plates 12 and 13 whileengaged and permits the driving plate 12 to rotate a substantialdistance ahead of the driven plate 13 during the interval between thestart of the axial separating movement of plate 12 and the completion ofsuch separating movement. During such interval the angle of engagementbetween the ball and pocket becomes gradually steeper to increase thetorque required for further separating movement. With this arrangement,the clutch may continue to run, without disengaging completely, whenthe. driven plate encounters a relatively high torque reaction over abrief interval of time, and responds only to a torque reaction which issustained throughout the interval necessary to complete the axialseparation of the clutch.

As shown in Fig. l, the increase in the radius of pockets 25 and 26above that of the balls 24, makes it necessary to reduce the arc of thepockets below degrees and therefore to reduce the cam angle at the edgeof the pocket where the ball completes its disengaging movement. Theinterposition of a conventional disc type retainer between the clutchplates 12 and 13 would make it necessary to reduce the arc and cam anglefurther with the resulting reduction in the maximum torque deliveredunder any given spring pressure. The present invention, which does notrequire the clutch plates 12 and 13 to be widely spaced to make room forthe retainer element, permits the pockets to extend over' an arc ofsufiicient size. The retainer sleeve 32 also assures uniform spacing ofthe balls not only during the overrun period while the balls are in theraceways 27 and 28, but also during the interval between the start ofthe clutch separating movement and the completion thereof, whichprovision of oversize pockets.

' serving to transmit torque from the driving plate to the driven platewith a camming component of force, resilient means holding the platestogether in driving relation with the balls seated in the pockets butyieldable upon camming action resulting from development of apredetermined torque to permit relative axial separation of the plates,said driving plate being adapted on separation to overrun the drivenplate and to re-engage upon reregistry of the pockets, and a retainercage for maintaining the balls uniformly spaced from each other duringthe period of overrun, said retainer cage comprising a cylindricalsleeve co-axially rotatable with the driving and driven plates, saidsleeve being received within registering cylindrical recesses in theclutch plates and being movable axially and rotatably with respect tothe walls of'the cylindrical recesses.

2. A torque release clutch according to claim 1, in which the sleeve hasa plurality of radial bores, each adapted to receive a ball, said boresbeing spaced ciranemia cumfcrentially by a uniform distancecorresponding to the circumferential spacing of the pockets.

3. A torque release clutch comprising a driving plate, a driven plate, aplurality of balls arranged between said plates to establish areleasable driving connection, and retaining means for maintaining theballs in uniformly spaced relation during rotation of the driving plateahead of the balls and driven plate, said retaining means comprising acylindrical cage having a plurality of radial ports each arranged toreceive an associated ball, said ports being uniformly spaced about thecircumference of the cage, one end of the cage being received within acircumferential recess in the driving plate and the other end of thecage being received within a circumferential recess in the driven plate,said cage being supported by the walls of the recess against radialmovement but having axial and rotative movement relative to the walls ofthe cylindrical recesses, such axial and rotative movement beingcontrolled by the position of the balls.

4. A torque release clutch comprising a driving plate and a driven plateco-axially rotatable, the adjacent faces of said plates being providedwith a plurality of approximately spherical pockets, said pockets beingspaced from each other by a uniform circumferential distance and beingdisposed at the same radial distance from the axis of rotation wherebyall of the pockets register simultaneously, balls received in saidpockets and serving to transmit torque from the driving plate to thedriven plate with a camming component of force, resilient means holdingthe plates together in driving relation with the balls seated in thepockets but yieldable upon carnming action resulting from development ofa predetermined torque to permit relative axial separation of theplates, said driving plate being adapted on separation to overrun thedriven plate and to re-engage upon re-registry of the pockets,

ball and of the annular groove or raceway connecting:

the pockets. 7

9. A torque release clutch according to claim 7, in which a chamfer isprovided on one edge of each pocket adjacent the annular groove orraceway, whereby the clutch releases at a lower torque in one directionthan in the other direction.

10. A torque release clutch comprising a driving clutch plate, a drivenclutch plate above the driving plate, a

and a plurality of means of maintaining the balls, uniformly spaced fromeach other during. the period of overrun, one of said means comprisinga. retainer element holding the balls against movement in acircumferential direction relative to each other and the other of saidmeans comprising a guide for confining the balls to a fixed orbital pathand for preventing movement of the balls in a radial direction relativeto the axis of rotation, said last named means including an annulargroove prow'ded on the face of one or both of the clutch plates andconnecting the pockets, said annular. groove providing a raceway for theballs during the overrunning action.

5. A torque release clutch according to claim 4-, in which each clutchplate is provided with a cylindrical recess connecting the pockets nearthe centers thereof, and in which the retainer element comprises acylindrical cage slidably fitted in said circumferential recesses, saidcage, being supported partly by the balls and partly by the walls of thecircumferential. recesses. 1

driving cup above the driven plate, means including longitudinal fingersextending between the driving cup and driving clutch plate to impartrotation from the cup to the driving plate while permitting relativeaxial movement, spring means urging the driving plate and driving cuptoward each other, the lower face of the driven plate and the upper faceof the driving plate being provided with a plurality of uniformly spacedpockets, balls received within said pockets and servingto transmittorque from the driving plate to the driven plate with a cam' mingcomponent of force tending to overcome said spring means to separate theclutch plates, s'aid driving plate being adapted on separation tooverrun the driven plate and to re-enga'ge upon re-registry of the ballswith the pockets, anti-friction meanslocated on top of the driven plateand ball raceways' connecting the pockets of both the driving and drivenplates and engageahle with the balls during the period of overrun, saidspring holding thef'driven clutch plate against axial movement relativeto the cup and in rolling contact with both the antifriction means andthe balls during the period of overrun.

11. A torque release clutch according to ciairn 10 which includes aretainer cage supported by the balls and arranged to maintain the ballsin uniformly spacedl relation.

References Cited in the file of. this. patent- UNITEDSTA' IES PATENTSCoddington ..;.Q Aug. 21, 1 945 3 France Nov. 28 1955

